diff --git a/core/modules/system/tests/modules/session_test/lib/Drupal/session_test/EventSubscriber/SessionTestSubscriber.php b/core/modules/system/tests/modules/session_test/lib/Drupal/session_test/EventSubscriber/SessionTestSubscriber.php
index 4be74ae..c01f1b4 100644
--- a/core/modules/system/tests/modules/session_test/lib/Drupal/session_test/EventSubscriber/SessionTestSubscriber.php
+++ b/core/modules/system/tests/modules/session_test/lib/Drupal/session_test/EventSubscriber/SessionTestSubscriber.php
@@ -54,7 +54,7 @@ public function onKernelResponseSessionTest(FilterResponseEvent $event) {
       // https.php because form submissions would otherwise redirect to a
       // non-existent HTTPS site.
       if (!empty($is_https_mock)) {
-        str_replace('https://', 'http://', $response->getTargetUrl());
+        $path = str_replace('https://', 'http://', $response->getTargetUrl());
         $response->setTargetUrl($path);
       }
     }